One of the clock genes involved is the PER2 gene. PER2 has been associated with behavioral adaptation to environmental stressors in humans [10] and to enhanced alcohol intake in PER2 mutant mice [11]. In an exploratory analysis of the human PER2 gene, the latter researchers reported first evidence for an association of allelic variation in PER2 gene with drinking levels in humans, which was driven by single nucleotide polymorphism (SNP) rs56013859 carrying an A/G exchange in intron 3 at position 1071 bp downstream of the ATG site of PER2 (GI:1365471).
